To get the pokedex you need to go north of pallet town prof oak should stop you and bring you to his lab and then he will let you have a Pokemon. Choose a Pokemon then defeat your rival then go north of pallet town keep going until you reach viridian city go inside the pokemart and the cashier should give you a package for prof oak go back to pallet town and give the package to prof oak he will thank you and give you a pokedex. After becoming Pokemon champion if you have recorded 60 Pokemon in the pokedex prof oak will upgrade it to the national mode meaning you can now capture and own johto and hoenn Pokemon.
catch 80 Pokemon
You have to catch it
After you fill your whole dex and beat the E4.
you must have the national pokedex at search for it in the trall grass and catch it or trade it from firered or leafgreen
Firered and leafgreen both can catch different Pokemon but there pokedex is the same, here is some examples: magmar only in leafgreen not firered, oddish in firered not leafgreen, ekans in firered not leafgreen, bellsprout in leafgreen not firered, pinsir in leafgreen not firered.
you can't unless you get the national pokedex and trade for one in sapphire or ruby.
look in your pokedex
catch 50 Pokemon and talk to prof oak grt natnail pokedex and go back
You have to catch 151 pokemon to complete the pokedex.
After you catch 50 Pokemon, have Prof. Oak look at your pokedex. He will send an aid with the Exp. Share
You have to catch at least 60 Pokemon and you have to beat the elite four including your rivalyou get it from oak after you beat the elite four and the elite four champion
'First catch upto 60 Pokemon before beating the Pokemon league. Then after beating them you will be back in your house. When you get out prof. Oak will be waiting outside to give you your national pokedex. '